Current sensing is required for a large array of applications, including load current control e.g. for chargers for portable devices. In such applications, it is important to have available a fast and accurate measurement of how much current is flowing into the load, e.g. for a reliable operation and control of a voltage supply. For direct charging architectures, it is common practice to use an external resistor for measuring the charge current flowing into the battery. However, this method requires an additional pin for connecting the external resistor, and its precision crucially depends on the precision of the external resistor. In addition, attention must be paid to the design of the printed circuit board (PCB) for the direct charging architecture, the package, and the input amplifier in order to ensure high precision. Especially for low charge currents, issues of electromagnetic compatibility (EMC) and electromagnetic noise may impair precision of current measurement.
As an alternative to using external resistors, the charge current may be measured by matching a pass device that provides the charge current by a small replica in such a manner that a fraction of the charge current flows through the replica of the pass device. However, especially for small charge currents, precision of the ratio of the current flowing through the pass device and the current flowing through the replica cannot be ensured in conventional direct charging architectures, thus impairing precision of current measurement for small charge currents.